I recently encountered this problem. When I want to open colab page (https://colab.research.google.com/), it shows me a 404 error.
Sometimes it can load the page. But then it show this error message:
Unable to connect to the runtime
I asked this problem from ChatGPT and I followed all of its suggestion. But nothing changed.
Some (maybe) useful ChatGPT's checks is:
ping of colab is OK.
Invoke-WebRequest -Uri "https://colab.research.google.com/" -Method Get
returns status code of 200 with normal headers.
That means the path to the colab is OK but it show me these error using browser.
I changed my browser from Chrome to Firefox, but it was not useful.
I clear browser cache, but nope!
I used Incognito window, but nope!
I used VPN, but nope!
I cleared DNS cache and changed my DNS to Google DNS. It worked for 1 day. But it got the problem again!
It seems Google has recently restricted access to Colab from Iran (like almost every other service). Honestly, I'm a bit surprised it took them this long (considering they have cut Iranian access to most of their services years ago). They usually return a 403 error, but this time the error is 404.
Consider using another VPN if you already have tried VPNs. The restriction is not account-based, but IP-based.